It took a little over 6 years to build the Twin Towers in the original World Trade Center complex.

Quick Scoop: Timeline

  • Site work for the World Trade Center started in 1966, including the huge underground “bathtub” and slurry wall that held back the Hudson River.
  • Construction of the North Tower (WTC 1) began in August 1968.
  • Construction of the South Tower (WTC 2) started in early 1969.
  • The North Tower’s structure was essentially completed by December 1970, when the first tenants began moving in.
  • The South Tower’s structure was completed in 1971, with tenants beginning to occupy it in January 1972.
  • The entire original World Trade Center complex, including the Twin Towers, was formally dedicated on April 4, 1973.

So if you go from the start of major tower construction (1968) to the complex’s official opening (1973), it’s about 5 years. If you include the critical foundation and site-preparation work that began in 1966, the full effort to “build the Twin Towers” runs to roughly 6–7 years.

In forum discussions, people often summarize it as:
“About six years from early groundwork to opening day for the Twin Towers.”

Why it took that long

  • Massive foundation work: Building the slurry wall and excavating over a million cubic yards of soil was a huge engineering challenge on its own.
  • Height and scale: These were, at the time, the tallest buildings in the world, pushing construction techniques and logistics to their limits.

TL;DR

From first major site work in 1966 to official opening in 1973, the Twin Towers took about 6–7 years to build, with the towers themselves going up in roughly 4–5 years from 1968 to 1972–73.

Information gathered from public forums or data available on the internet and portrayed here.